Magnetic and transport properties of amorphous Ge-Mn thin films

The magnetic and transport properties are investigated in well-characterized Ge_1-xMn_x (x in at.%) amorphous semiconductor thin films for a large range of Mn compositions, prepared by using thermal co-evaporation onto oxidized Si or glass substrates held either at room temperature or quench condensed onto LN₂-cooled surface. Magnetic hysteresis measurements at room temperature show saturation occurring by 1 - 2 kOe for all samples. The temperature dependence of the magnetization between 4 K and 300 K, measured at an applied field of 15 kOe and for zero-field cooled condition, exhibit a concave shape, different from the usual Brillouin behavior. The saturation magnetization at room temperature is found to range from 0.5 to 7 emu/cc. The highest magnetic moment observed per Mn ion is 0.76 Bohr magneton (μ_B) at 4 K at an intermediate composition x = 38.5 %. At x = 16.7 % where detailed transport measurements are carried out, the anomalous Hall effect is observed at 300 K, and the temperature dependence of the Hall effect is rather complicated. The magnetoresistance, being ∼1 % at an applied field of 50 kOe, changes sign at around 200 K.